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Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelianagro-ecosystems
Citation:
Kizito, F., M. Dragila, M. Senè, J. Renée Brooks, F. Meinzer, I. Diedhiou, M. Diouf, A. Lufafa, R. Dick, J. Selker, AND R. Cuenca. Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelianagro-ecosystems. JOURNAL OF ARID ENVIRONMENTS. Elsevier Science Ltd, New York, NY, 83:69-77, (2012).
Impact/Purpose:
Having sufficient water for drought stricken crops is an important struggle in Africa. This paper demonstrates a mechanism where deep rooted shrubs are interplanted with important food crops in Senegal. When the leafy above group parts of deeply rooted shrubs are removed during the growing season, the roots continue to move water from deep soil layers but instead of this water moving out of the leaves, it moves into the surface soil where it is available to the interplanted crop species.
Description:
Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Js) at the 20 cm depth declined significantly during the dry season with diel changes in Js of ?0.6 to ?1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments.